The present invention relates to a fuel-air mixture heating device for use with an internal combustion engine of the type which heats the intake manifold by an auxiliary burner, thereby attaining the complete combustion of the fuel-air mixture.
In the conventional fuel-air mixture heating devices, a part of the intake manifold at the downstream side of the carburetor is heated by exhaust gases or by the water circulating through the cooling system, or the intake manifold is heated by a burner formed integral with the intake manifold. In the former devices, the intake manifold cannot be heated above 100.degree.C because the water in the cooling system will not rise above 100.degree.C. In the devices of the type utilizing the exhaust gases, a passage for the exhaust gases is provided in the wall of the intake manifold so that it is also extremely difficult to heat the fuel-air mixture above 100.degree.C. When the exhaust gases heat the intake manifold too much, the temperature of the exhaust gases drops to such an extent that the efficiency of the catalytic converter for purifying the exhaust gases drops. Thus both of the heating devices utilizing the exhaust gases and the cooling water are not so effective that some of the atomized fuel particles are delivered into the engine cylinders without being completely vaporized, resulting in the unsatisfactory fuel-air mixture distribution especially in case of a multi-cylinder engine. Consequently, the smooth engine operation is not ensured in case of the acceleration or deceleration. To overcome these problems, the rich fuel-air mixture must be delivered to the engine cylinders. In the fuel-air mixture heating devices of the type which heat the mixture by means of a burner formed integral with the intake manifold, a part of the intake manifold may be easily raised in temperature above 100.degree.C, but the combustion products from the burner are discharged into the surrounding atmosphere or recirculated through the air conditioning system for automobiles after they have been used to heat the intake manifold. Consequently, the combustion gases containing toxic components are directly discharged into the surrounding atmosphere or the compartment of the automobile if the combustion conditions in the burner are not satisfactory. The emission of the toxic pollutants must be prevented in view of atmospheric pollution and the safety of the driver and passengers.